1. Field of the Invention
The present invention generally relates to inverters, i.e. static converters from D.C. to A.C., supplying a high frequency current.
It relates more particularly to novel arrangements of the inverter, whereby the safety in operation is considerably increased.
2. Description of the Prior Art
In a prior French Pat. No. 2,180,584 of the applicant of the present invention are disclosed and described inverters designed to supply high frequency alternating currents and which incorporate m pairs of controlled rectifiers, m being a whole number at least equal to 1. These rectifiers, which are connected in series, are periodically made conductive or non-conductive by applying a signal from a trigger signal generator so that each controlled rectifier in turn excites a driving resonant circuit, which supplies alternating current to a load circuit. In such inverters, the interval T.sub.o between two successive triggerings of the same rectifier is made equal to a whole-number multiple pT of the period T of the alternating signal produced. The number p is selected to be greater than the number m of pairs of rectifiers so that the period T, which corresponds to the interval between the time at which a given rectifier is triggered and that at which the next rectifier is triggered, is always greater than the half period T/2 , which thus makes it possible for the non-conductive period T.sub.4 of the rectifiers in the inverter to be increased by p T/2- T.sub.3 and the frequency of the AC output signal produced by the inverter to be increased accordingly; T.sub.3 being the time during which the controlled rectifiers are conductive.
In certain applications of such inverters, for example in underwater acoustics, the load impedance into which the alternating output current feeds may be subject to considerable variations and, in the extreme case, may become of zero value, for example because of an accidental short-circuit, or may take an infinite value, for example as the result of a disconnection. Such variations have repercussions on the way in which the inverter as a whole operates, the emitted power being inversely proportional to the value of the load impedance. Such variations may thus cause faulty operation on the part of the inverter and may result in the destruction of the controlled rectifiers.
To overcome such disadvantages and to improve safety in operation, it is known, interalia from an article by R. THOMPSON entitled "An Audio-Frequency High-Power Generator Employing Silicon Controlled Rectifiers" which appeared in the IEE proceeding 1962, 19 B, pages 249 to 258 and in particular page 256 to associate with inverters auxiliary power limiting circuits which allow protection to be automatically provided for the various components of the inverters as soon as the resistive part of their load impedance reaches values of zero or infinity. This auxiliary circuit is connected in series with the source of supply current to the inverter.